1. Field of the Invention
The present invention relates to a screen printing machine, more specifically to a screen printing machine having excellent pattern forming accuracy.
2. Description of the Related Art
Screen printing machines have conventionally been known as one type of apparatus for printing on plate materials typified by substrates for fabricating printed wiring boards with inks to form print patterns on the substrates. Such type of printing machine is provided with a screen, a squeegee, a driving mechanism for horizontally moving the squeegee, a driving mechanism for achieving screen separation by lifting one side edge of the screen on a fulcrum secured at the opposing side edge, etc. In this printing machine, the squeegee is slid from a printing start side toward a printing end side on the screen on which an ink is loaded to apply the ink onto a plate material mounted on a printing table.
It should be noted here that during the squeegeeing motion, the printing machine also drives a driving mechanism for achieving screen separation to separate the screen from the plate material at the same time. After completion of printing, a scraper is slid from the printing end side toward the printing start side on the screen to scrape the residual ink on the screen back to the printing start side. By repeating the procedures described, a plurality of plate materials are designed to be printed successively.
However, if the squeegeeing motion and the screen separating motion occur with awkward timing, the pressure of the squeegee is concentrated on a certain part of the screen to stretch the screen at such part. If such slackened screen is used, coating films having nonuniform thickness are formed, causing reduction in the pattern forming accuracy.
In order to avoid such inconvenience, it is necessary to properly coordinate the screen separating motion with the squeegeeing motion, more typically to set the screen lifting speed depending on changes in the speed of moving the squeegee and so on.
However, it has been conventionally necessary for an operator to make adjustment of a driving mechanism for driving the squeegee and another driving mechanism for separating the screen independently on his own, requiring intricate and difficult procedures.